The invention relates to a mechanism for latching a rotary shaft, which mechanism is provided with a control arm, which at its one end is immovably connected to the rotary shaft and at its other end is coupled by a pivotal shaft to the end of a coupling piece, the other end of which is connected by means of a pivotal shaft to one end of an operating arm, which is rotatable about a pivotal shaft mounted immovably relative to the rotary shaft, the pivotal shaft between the coupling piece and the operating arm running parallel to both the pivotal shaft between the control arm and the coupling piece and the pivotal shaft mounted immovably relative to the rotary shaft, and being movable both into and out of the plane determined by both last-mentioned pivotal shafts, for latching or rotating the rotary shaft.
Such a mechanism is known from U.S. Pat. No. 4,202,572. In this case the control arm bears the bolt of a lock for an escape door, so that in normal circumstances the mechanism will always be in the latched position. If the escape door has to be used, the mechanism can be operated by a control unit in the form of a push-button, which on displacement acts upon the coupling piece and in so doing unlatches the mechanism, with the result that the bolt releases and the escape door can be pushed open by hand. The escape door will then swing into the open position in quite an uncontrolled manner.